1. Field of the Invention
The present invention relates to a decoding apparatus for image codes, and in particular a decoding apparatus for image codes obtained by two-dimensional encoding such as modified READ (MR) encoding or modified modified READ (MMR) encoding.
In image transmitting apparatus such as facsimile or image files utilizing optical disks or magnetic disks, high-speed and efficient transmitting or accumulating operation is achieved through compression of image data.
For such compression of image data, MR and MMR encoding processes are generally known as disclosed in the Notification Nos. 1013, 1981 of the Japanese Ministry of Postal Service for two-dimensional encoding process and in the Notification Nos. 197, 1985 of the Japanese Ministry of Postal Service for high-efficiency two-dimensional encoding process.
In two-dimensional encoding, such as MR or MMR encoding, the codes represent the relationship between the image signals of a line to be encoded and the image signals of a preceding line. Consequently the decoding of such two-dimensionally encoded image codes necessitates a complex process for discriminating the relationship between the input image codes and the already decoded image signals of a preceding line, and such process has been conducted by means of software in, for example, a microcomputer. Thus the discrimination of an image code sometimes requires several steps. Therefore high-speed decoding operation is sometimes not possible since a succeeding image code may not be decoded immediately.
Also in two-dimensional encoding such as MR or MMR encoding, the length of obtained image codes is not necessarily uniform. Consequently, after a decoding operation, in order to prepare a succeeding code ready for decoding, the succeeding code is taken in according to the length of already decoded code. However, if the decoding time is short in comparison with the code length, the decoding operation may be interrupted since the succeeding code may not yet be ready for decoding when the decoding operation should be initiated.
Also in the two-dimensional encoding such as MR or MMR encoding, the relationship between the image signals of a line to be encoded and those of a preceding line is represented by codes of plural modes, and, in the horizontal mode among such plural modes, there are required an identification code indicating the horizontal mode and plural codes indicating the run length. Thus the horizontal mode is discriminated by the identification code, and the run length is identified in a following step. However, the decoding operation may be interrupted in such operation, since a succeeding code cannot be processed immediately if the run length is short.
The encoded image signals are decoded as explained above, and the decoded image signals are then supplied to a process unit such as a printer. However, in a case in which there are provided plural process units, it has been necessary to provide plural decoding circuits respectively matching the speeds of said plural process units or to provide a buffer memory for speed matching.